Comparative study on the mutated xylose reductase to increase ethanol production in xylose-utilizing Saccharomyces cerevisiae strains

We constructed one wild-type xylose reductase (XR) and eight XR variants in a recombinant industrial Saccharomyces cerevisiae strain along with xylitol dehydrogenase and xylulokinase overexpression. In the current study, we found that K270R XR (hereafter referred to as “XR-1”) appeared to utilize more NADH than NADPH when xylose was the carbon source. After 72 h of fermentation, XR-1 produced an ethanol yield of 0.34 g/g and a xylitol yield of 0.08 g/g from 55 g/L xylose, while it gave an ethanol yield of 0.44 g/g and a xylitol yield of 0.04 g/g under a mixture of 40 g/L xylose and 40 g/L glucose. Notably, the findings presented here suggest that the XR-1 variant produced approximately 76% more ethanol from xylose than the wild-type XR strain. Comparing with other widely divergent XR mutations, the XR-1(K270R) exhibited improved xylose consumption rate, balanced redox system and increased ethanol yield and production rate when engineered into S. cerevisiae, suggesting the significance of mutations to the XR gene in xylose utilization.

► K270R XR strain produced an ethanol yield of 0.34 g/g from xylose after 72 h. ► K270R XR strain gave an ethanol yield of 0.44 g/g from mixture of glucose and xylose after 72 h. ► K270R XR strain is an excellent producer of ethanol from xylose among 8 different mutated XR strains.